Machines using motors, as typified by hybrid automobiles, electric automobiles, and the like, utilize electric power conversion devices for saving energy. For the electric power conversion devices, semiconductor modules are widely utilized. The semiconductor modules include power semiconductor elements to control high current.
Power semiconductor elements generate a large amount of heat when controlling high current. Additionally, downsizing and weight reduction of semiconductor modules are demanded, and output density tends to increase. Thus, in a semiconductor module including a plurality of power semiconductor elements, a cooling method therefor influences electric power conversion efficiency.
In order to improve cooling efficiency for a semiconductor module, a liquid-cooling type cooler is conventionally used. Such a liquid-cooling type cooler incorporates fins as a heat sink and cools by causing a cooling liquid to flow in the cooler in a circulating manner. For liquid-cooling type coolers, various efforts have been made to improve cooling efficiency, such as increase in flow rate of a cooling liquid, improvement in heat transfer rate by miniaturization and complication of fins, or increase in heat transfer rate of a material constituting fins.
However, in a case where the flow rate of a cooling liquid into a cooler is increased or fins are formed into a shape having high heat transfer rate, disadvantages tend to occur such as increase in pressure loss of the cooling liquid in the cooler. Particularly, in a cooler having such a structure that uses a plurality of fins to cool multiple power semiconductor elements, in which the fins are arranged in series in a flow path (Patent Document 1), pressure loss significantly increases. In order to reduce such pressure loss, it is necessary to have a structure that increases cooling efficiency at a small flow rate of the cooling liquid, where the fins are desirably arranged in parallel in the flow path.
As coolers that maintain coolability and reduce pressure loss of a cooling liquid by parallel arrangement of fins in a flow path, there are those in which an inlet path for introducing a cooling liquid and an outlet path for discharging the cooling liquid are arranged in parallel to each other in a case and a plurality of fins are arranged in parallel in a cooling flow path(s) between the paths (Patent Documents 2, 3, and 4).